The present invention refers to an embossing device for planar materials, more particularly in the form of strips or bands, including at least two embossing rolls, i.e. a first, driven roll and a mating roll, which are arranged in parallel to each other in a mount and capable of being aligned in a position of defined mutual contact, and which is preferably used for the packaging of tobacco products.
Embossing devices of this kind are e.g. used in the packaging industry for the purpose of embossing packing materials while seals, devices, etc. are preferably stamped at the same time. In this context, the term embossing means providing the surface with a fine pattern in the millimeter and the submillimeter range. Sheet packing materials of this kind are e.g. used for the packaging of tobacco products (cigarettes), foods, chocolates, chewing gums, etc. An embossing device for this purpose is described in U.S. Pat. No. 5,598,774 of the same applicant.
The requirements with respect to such embossing devices, such as high operating speeds (e.g. 1.8 m/s), a fine, absolutely regular pattern, as well as an otherwise faultless embossing over prolonged, continuous periods of operation require a high precision in the construction and the installation of such embossing machines. Therefore, in the embodiments of the prior art, the entire so-called embossing head, i.e. a mount in which the embossing rolls are supported and which includes an adjusting device, inter alia, is attached to the embossing machine as an external component. These embossing heads may weigh more than 50 kg in some cases.
However, since the rolls are exposed to a calculable wear, regular servicing of the embossing heads is necessary. In particular, the rolls have to be exchanged from time to time. But the conversion e.g. to a different surface structure, a different seal or a different format also requires an exchange of the rolls. With the embossing heads of the prior art, this implies removing the entire embossing head, bringing it to a workshop where the necessary work is done, remounting the embossing head, and possibly effecting an additional, time-consuming readjustment on account of the inevitable loss of the adjustment involved in the process. Such an operation may take several hours, and due to the heavy weight, at least two people or additional lifting equipment are required in order to remove the embossing head and to remount it to the packaging machine.
For a quicker changeover, it is convenient to have a second embossing head ready. However, on one hand, this solution is very expensive financially, and on the other hand, it does not eliminate the need of precisely adjusting the newly mounted embossing head to the material feed in the packaging machine.
U.S. Pat. No. 5,590,557 discloses a roll stand for a pair of rolls which is arranged in a cassette, thus allowing an easy exchange of the rolls. The cassette comprises spindles in order to allow a precise mutual adjustment of the rolls, which is a problem in installations of that kind, but of no importance in the present device.
On the background of this prior art, it is the object of the present invention to provide an embossing device of the mentioned kind which allows an easier exchange of embossing rolls without requiring a pre-adjustment.
This object is attained by an embossing device wherein at least one of said embossing rolls is contained in an interchangeable unit, wherein the interchangeable unit comprises retaining means, and wherein said mount comprises seats whose shape is essentially complementary to the retaining means, so that the interchangeable unit is insertable in a predetermined position in said mount by inserting the retaining means in the associated seats. The further claims indicate preferred embodiments.
The invention is based upon the discovery that it is not absolutely necessary to support the embossing rolls directly in the mount of the embossing device. The driven embossing roll is coupled to the driving unit of the packaging machine, and it must be precisely adjusted to the feeding direction of the embossed material.